摘要
我国自从七十年代引入美国大地卫星多光谱象片(以下简称卫片)以来,鉴于解译方法大多局限于目视判读的定性分析,因而大大限制了卫片信息的提取与应用效果。目前,国内遥感信息的电子计算机自动处理技术,尚未普遍开展。能否在现有设备条件下,将解译工作定量化,使解译精度有所提高呢?这是本文以琼州海峡幅卫片为例探讨的第一个课题。此外,卫片为海岸动态的研究提供了有力的手段,已引起重视。但是,近岸海域的影象特征到底是哪些海洋要素的反映,尚有不少疑处。这是本文拟阐述的第二个课题。
The reflectance characteristic of a ground feature is the basic criterion for its discrimination on an aerospace imagery.On the Landsat photograph covering the area of the Qiongzhou Strait,along four lines running N-S,we chose 50 sample points lying at equal distance from each other.We measured with a scanning micro-densitometer the respective density of each sample point on the four negatives corresponding to Band 4,Band 5,Band 6 and Band 7 respectively.Thus we got 4 density values for each point(N_(4),N_(5),N_(6),and N_(7))and plotted them against the spectral band number to form the reflectance curve of that point.As similar objects on the ground have similar reflectance characteristics,so we can use the latter as a criterion to classify the ground features at these 50 points.The procedure is first using the cluster analysis statistical method to calculate the distance between the different sample points,and then group them according to the closeness of their spectral characteristics.The calculation was carried on with a simple electronic calculator.We found that these 50 sample points fell on the following types of ground features:sea water of different turbidity;platforms of lava flows extruded in different times;different terraces of accumulation;Siand spits;beach ridges;river beds etc.At the western end of the Qiongzhou Strait,a tidal delta spreads like a fan.It appears clearly on the Band 5 Landsat photo.But the regression analysis showed that there is no strict correlation between the density values and the depth values over the tidal delta.This is because the density values reflect directly the turbidity of the water,which is a function of both the intensity of the waves and the depth of water.Though the water is often turbid over the shoals where the waves touch the bottom,but during offshore winds,the nearshore zone might be free from waves so that the water remains limpid.Such was the case along the western coast of the Leizhou Peninsula when the photo we used was taken.On Band 5 photo the nearshore zone of that coast appears dark.The spectral characteristic of submerged reef flat is similar to that of clear water.The only difference is that the density values on Band 4 and Band 5 negatives of the former are higher than those of the latter.This is the result of ecological conditions of coral reefs.Bare silty mud tidal flat and mangrove forest tidal flat can be differentiated by comparing their tonal difference on negatives of different spectral bands.Both the eastern coasts of the Leizhou Peninsula and the Hainan Island are straightened by heavy accumulation.There are large-scale barrier beaches with silty mud tidal flat behind them.On these tidal flats mangrove forests are growing.Along the western coasts the coastlines are more indented and more stable.Coral reefs are widespread there.
作者
任明达
Ren Mingda(Beijing University)
出处
《海洋与湖沼》
1981年第3期210-224,共15页
Oceanologia Et Limnologia Sinica
